Field of the Invention
The invention relates to an apparatus and method of register correction having a device for turning a flexible plate about a point on a plate cylinder, and devices for effecting adjustments in circumferential and side registers of the plate.
A device is known from German Published Non-Prosecuted Application (DE-OS) 35 41 222 for correcting the canting of a flexible plate on a cylinder. This heretofore known device includes a bearing block with a clamping element for firmly holding one end of the plate. The clamping element is formed with slots for receiving pins of a mounting block. Due to the arrangement of the slots, it is possible to turn or twist the clamping element on the cylinder, so that a canted position of the plate can be corrected. A canted position of a plate on a cylinder of a is determined with reference to a plate on the cylinder of another unit of the same machine A disadvantage of the aforesaid device lies in the fact that although it is possible merely to correct a canted disposition of a plate, it is not possible with this device to turn the plate about arbitrarily selected points on the plate in order to achieve perfect registration correction.
In machines using plates mounted on cylinders, for example in presses wherein a separate pattern is formed in a separate unit of the machine, it is of utmost importance that all patterns are in perfect registration, or else a blurred or distorted pattern will be produced. Conventional presses have in each unit a side register and a circumferential register for adjusting the position of the plate in circumferential and side direction, i.e. lateral and transverse direction. In addition, conventional presses have some means for making minor angular adjustments for a plate if it for some reason has been installed on the cylinder in a skewed or canted position. In large presses, especially presses of the web-fed offset type, it is very undesirable to stop the press to make adjustments, because during a stoppage liquids on the cylinders will start to dry and cake, and upon restart dried liquid will cause streaks and runs in the patterns.
Furthermore, it is generally known, especially in the case of web-fed presses, to correct an inclined or skewed position of a plate by adjusting the mountings of the cylinder to an inclined or skewed position in accordance with the angle of the inclined or skewed position of the plate. Although this makes possible a correction to the skewed position of the pattern, the movement of the cylinder causes a distortion in the pattern to the extent that a rectangular pattern is produced with a parallelogram-shaped shift.
It is an object of the invention to provide an apparatus and method of registration correction which affords a material improvement over heretofore known apparatus and methods of this general type.
With the foregoing and other objects in view, there is provided in accordance with one aspect of the invention, a method of registration correction which includes turning a flexible plate about a given point on a cylinder of a press, wherein the method comprises the steps of determining data relating to deviation from proper registration of a defined register point on the plate in at least one of the circumferential, side and angular position of the flexible plate, by means of a specimen pattern made from the plate, and entering the data as adjustment commands for effecting adjustment operations in devices provided in the press for respectively turning the flexible plate about said point on the cylinder and for effecting circumferential and side registration, wherein the adjustment commands take into account not only the determined data but also the location of the point on the plate cylinder about which the plate is turned, so as to completely correct the registration of a pattern made by the plate.
In accordance with another aspect of the invention, there is provided an apparatus for performing a method of register correction having a device for turning a flexible printing plate about a point on a pate cylinder of a printing press, and devices for effecting adjustments in circumferential and side registers of the flexible printing plate, further comprising a device for determining data relating to the location of a register point and register deviations of the printing plate in circumferential and side position and angular position thereof, a computer for linking the determined data with conditions of a given point about which the printing plate is turnable and for establishing respective adjustment commands for the adjustment effecting devices, and devices communicating with the computer for receiving the adjustment commands from the computer for correcting circumferential and side registration and correcting angular registration by turning the printing plate on the plate cylinder.
The invention considerably simplifies the adjusting operations for attaining proper in-registration printing. It has been necessary, heretofore, with reference to a first specimen print, to determine the inclined or skewed position of the printing plate and to straighten the latter and, then, after a further specimen print, to determine and correct the side and circumferential-register offset. Now, the data for circumferential and side registration as well as for angular registration are established and the correction performed after just one specimen print. The ensuing specimen print then shows a correct printed image.
An essential advantage of the invention is both a saving in time when setting up and also a reduction in the amount of waste which is produced.
Misaligned or mutually skewed printed images in individual printing colors may be due to various reasons. In the manufacture of a printing plate, it may happen, for example, that an image which is to be transferred onto the printing plate is projected onto the printing plate out of alignment or canted with respect to the alignment of the printing plate. Furthermore, under certain circumstances, if the printing plate is not properly clamped into the holding or supporting device of the printing plate cylinder, the printing plate may be clamped out of alignment or canted. Such a misalignment or canted position with respect to the printing plate of another printing unit in a multi-color printing press cannot be compensated for only by side and circumferential register adjustments, but can at best be reduced only to a lesser error.
An operator will detect such an error, for example, by detecting good registration in one area of a printed image and a registration deviation in another area. The printing plate must then be turned about a point in the area of good registration. From the area of registration deviation it is possible, with reference to the register center of rotation, to determine an angular adjustment of the plate, in magnitude and direction. Because the printing pate, for reasons of construction, can be turned only about a precisely defined center of rotation on the printing-plate cylinder, it is necessary, after turning the printing plate about this center of rotation, to compensate for the resultant shift in side and circumferential register.
If there is both side and circumferential and angular misalignment of a printing plate, then an area of proper registration cannot be detected on the printed image. In this case, the deviation of all three values to be corrected must be determined either by means of registration marks or directly from the registration error in the image.
A further advantage of the invention stems from the fact that certain areas of an image can be declared as vital areas, so that the registration of the plate can be performed especially for these areas.
In accordance with a further feature of the invention, input apparatus is provided for entering the registration data, wherein this input apparatus includes a data input panel. The data input panel has an area which corresponds to the printed image in either the same or a different scale. Such an input panel permits a particularly simple entry of the registration data in that the position of the registration point on the printed product can be entered identically with regard to its position, into the input panel. Likewise, the magnitude and direction of the angular adjustment can be entered into the input panel in the manner of a graphic input. Of course, it is also possible to enter registration data numerically into the input panel.
In accordance with another feature of the invention the input panel has different scale factors for the x and y-directions, in relation to the printed product This is particularly advantageous if, for example, there is only a small and limited space available on a control console of a printing press or if an existing input panel of given dimensions is to be used for entering the data.
In accordance with still another feature of the invention, the input panel is in the form of a sensor array, wherein the data are entered by means of image corresponding sensors, for example by depressing or touching sensor keys or by means of contactless inductive entry.
In accordance with an additional feature of the invention, a display array is located below the sensor array for showing the positions of the registration data that have been entered so that, as the data are being entered, they are displaced simultaneously, making it possible to make correction immediately to any data that may have been incorrectly entered. This display is particularly useful if, for example, the magnitude of an angular adjustment is entered graphically e.g. as a chord between two sides of a triangle.
In accordance with yet another feature of the invention an ink zone display and input system, of the kind used in a majority of remote-control consoles for controlling a printing press, is used as a control console for entering registration data according to the invention. Such a so-called ink zone display shows an ink density profile for the entire printing width and is formed, for example, of a multiplicity of rows and columns of light-emitting diodes, with each column being assigned to an ink-metering element and the length of each column representing the magnitude of the ink gap of the ink-metering element. The ink gap of an individual ink-metering element is indicated by the illumination of one or more light-emitting diodes in a column. By means of keys or other controls, the respective ink gap and the corresponding display can be altered. Such an ink zone display can be used advantageously to enter the data for turning the printing plate. In this case, the width of the ink zone display represents the width of the printing plate, while the length of the printing plate is represented by the length of the columns of light-emitting diodes. It is in this way possible to activate a sensor element corresponding to the position of the register point and the light-emitting diode corresponding to it and to enter and/or display the direction and magnitude of the turning angle, for example, by energizing several sensor elements, with their light-emitting diodes in a column. Of course, it is necessary, prior to such entering of the data to change the input mode and to select the printing unit in which the plate is to be turned.
It is also possible that respective display and input panels which are present on a control console of a printing press, for the purpose, for example, of adjusting the registers in the individual printing units, to be used for the graphic entry of registration data.
In accordance with yet a further feature of the invention, a light pen is used for entry of registration data. The light pen can be used on a sensor panel for entering the position of the register point and the turning angle by means of suitable light-sensitive sensors. Of course, it is also possible to use instead of a light pen an input device cooperating, for example, via an inductive coupling with the input panel, as well as to use a photoelectric-barrier grid instead of an input array, which has the advantage that no auxiliary devices are required for entering the data. In addition, a plurality of pushbuttons and keys may be used for data entry.
In accordance with a concomitant feature of the invention, the printing plate is mounted at its two ends in holding or supporting rails which are turnable and displaceable, wherein the turning of the printing plate is effected by turning the rails.
The turning motion may be accomplished, for example, by an electric motor or hydraulically by means of apparatus described in detail in copending U.S. patent application Ser. No. 013,010 filed Feb. 10, 1987 of applicant, now allowed. Return information on the turning motion may be transmitted by means of suitable sensors connected to the corresponding actuator or adjustment element.
The side and circumferential-register correction may similarly be accomplished in conventional manner with suitable actuators, for example servomotors. In an advantageous manner, already existing servomotors for the side and the circumferential registers are used for this purpose.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in apparatus and method of register correction, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.